Hi Colin,
There are 2 answers to your question. The first which is a direct answer to your question is Yes. True Tombak is an alloy of 82% copper, 8% tin, 7% zinc and 3% lead, ( source, Deutsche Industrie-Norm) and has a bronze color. Zinc badges on the other hand are encounted in either what is refered to as "finezinc" a refined zinc alloy or the later "Kriegsmetall" which was a very low quality alloy. both have a grey apperance with the Kriegsmetall being a very dark grey.
The other answer is that badges ,especialy Luftwaffe were made from other materials "neusilbe" and "altsiber" being 2 . Read Andy Hopkins excellent article on badge construction here;
http://www.wehrmacht-awards.com/coll...nstruction.htm